Add full compiler toolchain, libc, examples and reference docs

First substantive commit: the entire Sprinter C compiler tree on top of
the bare README+gitignore initial commit.

What's in here:
  bin/sprinter-cc        — driver script invoking SDCC + linker + mkexe
  libc/                  — Sprinter-specific libc layer over ESTEX/BIOS
                           (conio, gfx, io, mem, stdio + headers)
  runtime/               — crt0 variants (default/small/banked/minimal)
                           + heap + bank trampolines
  toolchain/             — mkexe (SprintEXE packer, C + tests)
  examples/              — 30 demo programs (gfx, file I/O, env, time, …)
  lib/Makefile           — builds the libc archive (sprinter.lib)
  docs/                  — converted Sprinter manuals + asm reference samples
  third_party/           — solid-c reference compiler dump + sdcc setup script
  release_docs/          — packaging / release notes

gitignore overhaul:
  • Drop dangerous blanket patterns: *.asm (would hide docs/samples/*.asm)
    and *.exe (case-insensitive match was hiding third_party/solid-c/*.EXE
    on macOS APFS).  Replaced with examples/*/*.{asm,exe,…} and lib/*.lib.
  • Restore tracking of toolchain/mkexe/tests/{one,big}.bin — those are
    INPUT fixtures, not build outputs.
  • Collapse the duplicated SDCC/C/Sdcc sections into one section per
    concern (build outputs / vendored / OS-junk).
  • Add .sprinter-cc-*/, build/ (catches lib/build/ too), .claude/.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/samples/aprint/readme.eng

@@ -0,0 +1,79 @@
+    The tutorial procedure for colour printing at the graphic screen 640x256x16.
+
+                 This procedure was used in the Flex Navigator v1.xx.
+                       Written for Estex v1.xx or high.
+
+Files description:
+	main.z80  - initial(main) file
+	print.z80 - printing procedure
+
+Font format description:
+  In the font used 256 symbols with height 8 points and various width.
+
+  +000 [256] - width of a symbol on X (for each symbol) (in bytes)
+  +256 [256] - low byte of symbol image offset (for each symbol)
+  +512 [256] - high byte of symbol image offset (for each symbol)
+  +768 ...   - images of symbols (from 0 to 255 symbol)
+	       images stored as vertical lines, 8 bytes per line, 4 bits per point.
+	       number of lines (in bytes) calculate from size of X
+               background colour = 0x00
+	       foreground colour = 0x0F
+
+	       for instance, image of "A" symbol:
+		width of symbol on X = 4 (bytes)
+	        00 00 00 00
+	        00 FF FF 00
+	        0F 00 00 F0
+	        0F 00 00 F0
+	        0F FF FF F0
+	        0F 00 00 F0
+	        0F 00 00 F0
+	        00 00 00 00
+
+		In the image of symbol it will stored as:
+
+		00 00 0F 0F 0F 0F 0F 00  00 FF 00 00 FF 00 00 00  00 FF 00 00 FF 00 00 00  00 00 F0 F0 F0 F0 F0 00
+		
+Algorithm description:
+  The main problem for the colour printing was fast transformation each point (background/foregraunf) to the necessary colour.
+Here, I will showed, how I could solve this a "hard" problem. ;) If somebody will think up faster variant, I will be glad to see it. :)
+
+  The printing on the screen realized by vertical lines with the help of accelerator at once till 8 bytes.
+We require 2 buffers, size in 8 bytes for the colors mixing (background and foreground). Because, to get mixed up we shall be at once till 1 vertical line. These buffers are initialized at each change of colour by function PreparePrintColors (It's made automatically and you don't need about it to care!).
+
+Using print by function TextOut.
+
+	operation | - Logical Inclusive OR (in Z80 CPU instruction OR)
+	operation ^ - Logical Exclusive OR (in Z80 CPU instruction XOR)
+
+Function PreparePrintColors:
+
+	1. initialize ForegroundBuffer
+		ForegroundBuffer = Foreground colour ^ 0xFF
+	2. initialize BackgroundBuffer
+		BackgroundBuffer = Background colour ^ ForegroundBuffer
+
+Function TextOut (input parameters see in the source):
+	actually, a image printing:
+	Screen = (line_of_image | BackgroundBuffer) ^ ForegroundBuffer
+
+Let's look at a point level:
+	assume the colors for printing Background = 0, Foreground = 1
+
+	then ForegroundBuffer = 1 ^ 0xFF and result 0xFE
+	also BackgroundBuffer = 0 ^ 0xFE and result 0xFE
+
+	for the background colour from a image (=0x00)
+	Screen = (0x00 | 0xFE) ^ 0xFE result 0x00
+
+	for the foreground colour from a image (=0xFF)
+	Screen = (0xFF | 0xFE) ^ 0xFE result 0x01
+
+It's possible to do for any of colours...
+
+This algorithm works slower when are printed of very small strings. It occurs because a lot of initialization are required. Also when made often change of colour (Though, I hadn't changing it in the Flex Navigator so often, only for necessary). ;)
+
+27 june 2002
+Anton Enin (C) Copyright 2002 R-lab
+If you have the questions email me: r-lab@mail.ru or ask in the Sprinter's forum.
+